That depends. You trigger a filter check through search engines and your ISP who then have to legally inform the authorities. You then get a file opened on you, and depending on your profile, you either get spied or have police visit you.
If, for example, you're a young edgelord teenager who searches for bomb recipes and downloads games like Hatred, and your dad has guns in the house, and you post things on social media that hint at violent action, then you will likely get a swift visit from the police. If, on the other hand, your profile is that of someone older with a career and life, then they passively spy on you and only intervene if they have evidence that you're going to take action against the government, like trying to organize a resistance group to conduct attacks. They won't intervene right away, of course, they'll infiltrate the group and gather as much intelligence as possible, right up until the moment you give orders to commit some act of domestic terrorism. If your organized group is not militant in nature and won't risk conducting attacks, then they'll put you in some rogue category like a non-violent hate group and they'll keep spying on your for life basically.
Government spying is ruthless and efficient. Always assume that they're watching, because 999999/1000000 times, they are. If you plan on anything you don't want governments to know about - even if it's just talking - never carry electronics with you of any kind, ever, and have 100% trust in the people you're with, because they will be your security leak, if discovered.